There are numerous methods and systems for detecting radiation. In one type of detector, photocathodes are used in conjunction with microchannel plates (MCPs) to detect low levels of electromagnetic radiation. Photocathodes emit electrons in response to exposure to photons. The electrons may then be accelerated by electrostatic fields toward a microchannel plate. A microchannel plate is typically manufactured from lead glass and has a multitude of channels, each one operable to produce cascades of secondary electrons in response to incident electrons. A receiving device then receives the secondary electrons and sends out a signal responsive to the electrons. Since the number of electrons emitted from the microchannel plate is much larger than the number of incident electrons, the signal produced by the device is stronger than it would have been without the microchannel plate.
One example of the use of a photocathode with a microchannel plate is an image intensifier tube. The image intensifier tube is used in night vision devices to amplify low light levels so that the user can see even in very dark conditions. In the image intensifier tube, a photocathode produces electrons in response to photons from an image. The electrons are then accelerated to the microchannel plate, which produces secondary emission electrons in response. The secondary emission electrons are received at a phosphor screen or, alternatively, a charge coupled device (CCD), thus producing a representation of the original image.
Another example of a device that uses a photocathode with a microchannel plate is a scintillation counter used to detect particles. High-energy particles pass through a scintillating material, thereby generating photons. Depending on the type of material used and the energy of the particles, these photons can be small in number. A photocathode in conjunction with a microchannel plate can be used to amplify the photon signal in similar fashion to an image intensifier tube. The detector can thus be used to detect faint particle signals and to transmit a signal to a device, e.g., a counter, that records the particle's presence.
A photocathode may include one or more layers of material deposited or grown on a surface or substrate of the photocathode to provide anti-reflection properties, filtering properties, electron transportability properties, and other suitable properties associated with the photocathode. After the layers have been deposited or grown on the surface of the photocathode, the surface of the photocathode generally requires polishing to reduce the layer to a predetermined thickness to provide the desired photocathode properties. The polishing process generally includes translating the photocathode across a polishing pad and/or polishing compound for a predetermined amount of time. Thus, the amount of material removal from the photocathode is a function of the abrasive characteristics of the polishing pad and/or chemical etching properties of the polishing compound, the amount of pressure applied to the photocathode during polishing, and the amount of time the photocathode is polished.
Various types of processes may be used to polish the photocathode. An example polishing process may include applying a polishing compound to a polishing pad and translating the photocathode across the polishing pad and polishing compound for a predetermined period of time. After the predetermined time period has elapsed, the photocathode may be removed from the polishing compound and transported to a rinsing station where excess polishing compound may be removed from the photocathode.
However, prior systems and methods for manufacturing a photocathode suffer several disadvantages. For example, chemical properties of the polishing compound may cause oxidation of the photocathode as the photocathode is removed from the polishing pad. As a result of the oxidation, the photocathode may require additional processing to remove the oxidation or the photocathode may be unsuitable for various applications.